Averaging device



April 26, 1949. A. L. HOLCOMB 2,468,200

AVERAGING DEVICE Filed June 2, 1944 3 Sheets-Sheet 1 LL Q,

/Nl/ENTOR By A. L.HOLCOMB A TTOPNE V April 26, 1949. A. L. HOLCOMB AVERAGING DEVICE Filed June 2, 1944.

3 Sheets-Sheet 2 FIG? lNl/E/VTOR By AL .HOLCOMB ATTORNEY Patented Apr. 26, 1949 UNITED STATES PATENT OFFICE AVERAGING DEVICE Arthur L. Holcomb, Tarzana, Calif., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application June 2, 1944, Serial No. 538,523

7 Claims. 1

This invention relates to averaging devices, and particularly to devices for averaging over a period of time the varying distribution of a liquid between any two containers such as the arms of an artificial horizon or U--tube.

The object of the invention is an averaging device of the type which is automatic in operation and well adapted for use in portable apparatus.

According to the general features of the invention, a valve interposed between the arms of a U-tube or other liquid containers, is opened at the beginning of an averaging period to permit free flow of the fluid to equalize the fluid pressures on its opposite sides but means is provided for progressively closing the valve at such a rate that when the valve is completely closed the final levels are the average of the various levels obtaining throughout the period. The valve may be operated in any suitable manner such as by a spring controlled by an escapement or other governing mechanism, and the desired averaging action is obtained by proper design of the valve orifice so that the time required to equalize a given pressure difierence between the liquid containers increases uniformly over the averaging period.

An important feature of the invention is a simple valve and valve operating mechanism in which a uniform time motion is translated into a reciprocal function of time over a relatively long period with a high degree of accuracy to produce the required averaging action.

This mechanism may be incorporated directly in the level or artificial horizon tube of a sextant or similar instrument in which case the pressures across the valve are due to the action of gravity on the liquid in the tube or it may be incorporated in auxiliary apparatus to provide for various measuring instruments an averaging attachment in which the pressures are generated according to the motion of an adjusting device on the instrument.

The auxiliary apparatus may take the general form of a closed U-tube containing fluid which is forced through the valve by means of bellows in the tube arms operated in accordance with the motion of an adjusting device on the instrument, such for example, as the tangent screw of a sextant. Any accumulated pressure difference existing between the arms at the end of the averaging period represents a correction to be applied to the initial reading taken before the release of the valve closing mechanism. This correction may be read from a suitable indicator and added algebraically to the initial reading or if desired the bellows may be driven through reversible mechanism so that the averaging correction is made automatically upon the release of the instrument adjusting device due to the energy stored in the bellows or in springs provided for the purpose.

These and other features of the invention. will be more clearly understood from the following detailed description and the accompanying drawings in which:

Figs. 1 and 2 are side and front views respectively of an averaging sextant according to the invention;

Fig. 3 shows the averaging valve and its operating mechanism;

Fig. 4 shows the averaging valve as used with indicating auxiliary apparatus; and Fig. 5 shows an automatic averaging attachment for sextants or similar instruments.

The sextant of Figs. 1 and 2 comprises a frame I on the back of which, as viewed in Fig. 1, is mounted sighting means such as the usual optical tube having an eye-piece 2 and an object lens 3 and on the front of which is mounted the artificial horizon tube 4 and averaging mechanism 5.

The horizon tube 4 is of essentially circular configuration half-filled with mercury 6 as shown. The two sections 1 and 8 in which the mercury levels vary With the angle of sight are interconnected by the valves 9 and [0 which are closed under the control of the mechanism shown in detail in Fig. 3.

In Fig. 3 the valve 9 is of any suitable type which can be closed at the proper rate in accordance with the requirements as explained below but in the form shown by way of illustration it comprises an outer casing II and a fixed inner cylindrical member I2 which together define an outer chamber I3, to which section 8 of the horizon tube is connected by a pipe I4, and an inner chamber l5 to which section 1 of the tube is connected by pipe IS. The hollow drum H, which in the assembled valve slides into the member l2, has a large opening l8 opposite the pipe l6 and a narrow slot l9 opposite the specially shaped slot 2% in the member 12 to provide a free passage between the pipes and i6 when the valve is open.

The valve is closed by rotation of the drum I! in a clockwise direction so that the slot [9 moves upwardly across the slot 20 to reduce the valve opening progressively until at the upper edge 2| it is entirely closed. When the valve is opened it is held in this position against the tension of a spring 22 by the pawl 23 engaging a toothed wheel 24 of the clock escapement mechanism 25. This mechanism may be of any suitable type which can be set into operation at will as by a push-button 25 to permit the spring 22 to rotate the wheel 24 at a uniform, controlled rate which will close the valve 9 during a predetermined sighting period such as 120 seconds.

In order that the closure of the valve shall result in producing in the sectors 'l and 8 final levels which are the true average of the various different values existing throughout the sighting period due to the oscillations of the optical axis about the true line of sight, it is necessary that the slot be contoured in such a way that the time required to equalize a given difference in the pressures is directly proportional to the elapsed time. If, for example, at the end of the first second the restriction in the valve orifice is such that a given pressure difference is equalized in one second, then at the end of the sighting period of 120 seconds, just before the valve is completely closed, the same pressure difference should require an equalizing period of a further 120 seconds. While the valve is closing, since both the area and shape of the orifice will be changing, the orifice coefiicient also will be changing and the equalization time therefore does not increase linearly with decrease in the actual orifice area. convenient to provide slots l9 and 20 of approximately the proper sizes and shapes and modify them slightly by empirical methods until the rotation of the shaft 28 varies the eifective orifice area as a reciprocal function of time to the required degree of accuracy. The effective orifice area may be defined as that which divided into the pressure difference gives a quotient proportional to the time required to equalize that difference, i. e.

where D is the pressure difference, Aeff is the effective orifice area and T is the time in which D is reduced to zero. If T is to be proportional, at any instant ii, to the elapsed time t1-to after an initial instant in, Aeff must be inversely proportional to t1to.

In using the sextant to determine the altitude of a celestial body the valve is fully opened by moving the handle 21 to the position shown in Fig. 3. A sight is then taken through the optical tube and maintained on the body as accurately as possible over the sighting period in the usual manner. In elevating the optical axis 3| to the sighting position the instrument is rotated in a counter-clockwise sense so that the mercury flows through the valve 9 from section 8 to section I of the tube 4 to reestablish the horizon. At the beginning of the sighting period when an approximately correct sight is first obtained, the valve closing mechanisinis set into operation by means of the pushbutton 25. The toothed wheel 24 then begins to rotate in a counter-clockwise direction as viewed in Fig. 3 permitting the spring 22 to drive the valve shaft 28 in a clockwise di rection through the pinion 29 and toothed seg ment 3!! of the handle 2?. The rotation of the shaft 28 rotates the drum I1 to close the valves 9 and It! under the control of the mechanism as already described.

At the end of the sighting period when the mechanism 25 has been stopped and the average levels of the mercury in the sectors 1 and 8 have For this reason, it will be been determined, the mercury is trapped by the complete closure of the valves 9 and [0 so that these final levels cannot be affected by careless handling of the instrument before the levels have been measured. While the valve 10 is shown as being of the same type as valve 9, it will be understood that in instruments such as sextants or octants only valve 9 is normally in the mercury path. It will therefore be understood that in such instruments the valve I0 is not necessarily of the averaging type.

In order to simplify the procedure of determining the horizon line with respect to the optical axis the tube sectors 1 and 8 may be of conducting material, such as carbon or they may contain high resistance wires so that the ratio of the resistances between the ends of the sectors or between the ends of the wires is a measure of the distribution of the mercury between the tube sectors and hence a measure of the angle between the artificial horizon and the optical axis. This ratio may be conveniently measured by connecting the tube sectors as arms of a conventional bridge as shown for example in Patent 1,506,192 to Meijer.

If, for any reason, such as when a very high degree of accuracy is not required, it is desired to limit the observation to something less than the full sighting period, the valves may be closed at will by operating the trip lever 32 to the right as viewed in Fig. 3. Lever 32 is pivoted about pivot 32, supported in anyconvenient manner from casing 5. This moves the pawl 23 to the left out of engagement with the teeth and onto the smooth portion 33 of the wheel 24, thereby freeing the shaft 34 from the escapement mechanism and permitting the spring 22 to close the valves without further delay. When the valves are closed and the trip lever is released the pawl 23 reengages the teeth of the wheel 24 to condition the mechanism for the next operation.

In the averaging device of Fig. 4 the shaft 40, may be connected to the tangent screw of a sextant or to any other mechanism to which the av-,- eraging action is to be applied. The motion of the shaft is transmitted through non-reversible gearing 4| and a clutch 42 to a spring 43 which converts the motion into a corresponding force which acts against the plunger 44 of the bellows 45. The bellows 45 and 46 are interconnected by a U-tube 47 in which there is an averaging valve 48 similar to the valve 9 of Fig. 3 operated by mechanism 49 which may be identical with the mechanism 5. The bellows 46 has a plunger 50 the position of which is registered by a suitable indicator 5|.

The bellows and U-tube are filled with any suitable fluid, such as ethyl alcohol which has substantially constant viscosity over a wide temperature range, so that rotary motion of the shaft til is converted into pressure changes on the fluid. While the bellows have the character'- istics of a spring which is undesirable in this device, they are preferred over conventional pistons since the latter would require the use of a lubricating fluid as the transmission medium and a lubricant of constant viscosity is not readily available. Since the bellows are driven through the spring t3 it is necessary to neutralize their spring characteristics to avoid error in the averaging process. This can be done by filling the system with the fluid, compressing both bellows to the mid-point of their linear compression travel to expel the excess and then sealing off the systems in this position. Under this condition the spring'characteristics of the two bellows will be equal and opposite over their working range so that'the operation is the same as if pistons were used.

In operation the shaft 40 is set to an approximate position as, for example, by a preliminary altitude measurement with an associated sextant, the clutch 42 is engaged, the valve 48 is opened and at some chosen instant the mechanism 49 is set into operation to begin closing the valve. While the valve is fully open the indicator 5| will follow the motion of the shaft 48 in either direction but as the valve closes in the manner already described for the structure of Fig. 1, the response of the indicator will be proportionately delayed and when the valve is finally closed the indicator is effectively locked in its averaged position. The value shown on the indicator is then added to or subtracted from the preliminary reading to obtain the final averaged reading.

'With the structure of Fig. 5 the necessity for the correction indicator is eliminated and the averaged reading is determined automatically by driving the averaging mechanism through reversible gearing 55. In general this structure is similar to that of Fig. 4 as indicated by the correspondingly numbered elements except that in this case, both bellows are connected to the driving gear 55 through a sprin 57 and a rack 58 and a spring 59 and a rack 50 respectively, In this push-pull construction the effects of temperature changes on the fluid within the bellows and U-tube and on the mechanical linkages are balanced out and all gear backlash is eliminated due to the fact that the springs and bellows are under some compression in any operating position as explained in connection with Fig. 4.

It should be noted that, although the structure of Figs. 1 and 2 requires the use of a liquid medium since the pressure differentials are derived from gravity, that is not true of this structure or the structure of Fig. 4. It is, therefore, quite feasible to fill the bellows with a gas under suitable pressure and when gas is used advantage may be taken of the compressibility of the gas to convert motion of the bellows into 2. corresponding force on the racks in which case the springs 43 of Fig. 4 and 51 and 59 of Fig. 5 may be eliminated.

4 In the operation of this device in connection with a sextant, for example, the sequence begins with the clutch 42 disengaged, the valve 43 fully open and the bellows 45 and 46 at about midposition of the chosen operating range so that the racks 58 and 5B are contacting the gear 56 at substantially their mid-points as shown. As in the previous case, a preliminary altitude is then set up on the sextant and the averaging sequence is started by engaging the clutch 42 and releasing the valve closing mechanism 49, During the sighting period the shaft 40 rotates or oscillates in following the adjustments of the tangent screw made by the operator in the attempt to keep the optical axis of the sighting tube on the true line of sight and the resulting rotation of the gear 56 moves the racks 58 and 65 in opposite directions to vary the distribution of the liquid between the bellows. As the opening of the valve 48 is progressively restricted in the averaging process, the accumulated energy in the springs 5'! and 59 due to the excursions of the tangent screw from the preliminary setting position always tends to move the tangent screw being held by the operator. When the tangent screw is released at the end of the sighting sequence or at any intermediate instant it will, therefore, move automatically to the accumulated average position which may then be read directly as in the case of an ordinary sextant.

While this construction requires the operator to hold the tangent screw against the accumulated difference in the spring tensions, this is not a serious objection since the force required to move the screw in a dependable manner need not be very large. Moreover, in the early stages of the period while the valve opening is still relatively large and the equalizing time is correspondingly short, the amount of energy stored in the springs is quite small. As the sequence progresses the springs will absorb a considerable part of the rack motion incident to wide excursions of the shaft 40 and the tangent screw, therefore, must be held against the force of the springs. However, any wide excursion from an accumulated average is likely to be an error due to an attempt to follow the bubble during some sudden motion of the ship or airplane from which the observation is being made. With most averaging devices such an error existing while the line of sight is being corrected would be averaged in with the more accurate sights.

This direct reading device, however, greatly facilitates observations in rough weather since, when a disturbance occurs, the navigator can release the tangent screw and permit it to return to the average accumulated up to that time. A few seconds later when conditions are more favorable a complementary averaging sequence may be started using the accumulated average as a starting point and in this way the large obser-- vation errors are prevented from producing any appreciable degradation in the final average,

From the above description, it will be apparent that the averaging mechanism of this invention is applicable to structures of various types and while several of these have been described for purposes of illustration, it will be understood that these structures may be modified in various ways within the scope of the following claims.

What is claimed is:

1. In a tube connecting two fluid containers in each of which a contained fiuid is subjected to a fluctuating pressure, means for determining the average difference over a desired time interval of the pressures in the containers comprising a valve provided with a variable aperture adapted to control the rate of flow of fluid through the tube, means for varying the aperture from a maximum to a minimum substantially reciprocally with time throughout the desired interval and means for indicating the final difference of the pressures at the end of the interval.

2. Means for determining the average difference over a desired time interval of pressures in a pair of fluid containers connected by a tube, each of said containers containing a fluid subjected to a fluctuating pressure, comprising a valve in the connecting tube composed of two cooperating members, one of said members being fixed and provided with an orifice communicating with one of the containers, the other of said memhere being provided with an orifice communicating with the other container and being movable with respect to said member to define therewith a variable orifice permitting a variable rate of fluid fiow between the containers, said second named orifice being so contoured that when said other member is moved throughout the time interval at a uniform rate with respect to said one member the defined orifice varies from a maxi- 1 mum to zero. substantially reciprocally with time, means for moving said other member uniformly with time throughout the interval and means for indicating the final difference of pressures at the end of the interval.

3. In a device. for determining the angular displacement of an object from. an artificial horizon, a U-tube containing a liquid varying in level with the angular position of the tube, a valve between the arms of the tube and means for progressively decreasing the efiective valve opening in accordance with the reciprocal of the elapsed time to average the levels of the liquid and for completely closing the valve at the end of a predetermined period to preserve the average value of the levels of the liquid.

4. In a device for determining the angular displacement of an object from an artificial horizon, a U-tube containing a liquid varying in level with the angular position of the tube, and means for averaging the levels of the liquid in the tube with respect to time comprising a valve interconnecting the arms of the tube, means for opening the valve and means for progressively closing the valve to restrict the flow of liquid at such a rate that the rate of flow of liquid through the valve varies substantially inversely with time during the interval of closing of the valve.

5. In a device for determining the angular displacement of an object from an artificial horizon, a U-tube containing a liquid varying in level with the angular position of the tube, a normally open valve in the portion of the U-tube connecting the arms thereof and having an operating shaft, means for rotating the shaft at a controlled rate to close the valve in a predetermined time interval, and means in the valve defining an orifice having an effective area which varies with the rotation of the shaft in accordance with the reciprocal of the elapsed time over substantially the Whole time interval required to close the valve.

6. Means for determining the average position of a movable member throughout a desired time interval comprising a pair of containers connected by a tube, fluid in each container subjected to a pressure varying with the position of the member, a valve in the connecting tube including a fixed element having an aperture communicating with one of the containers and a rotatable element having an aperture communicating with the other container and coacting in position with the fixed element to define an orifice of variable area permitting transfer of fluid between the containers at a variable rate, the apertures being so contoured that the rate is reciprocally proportional to the rotation of the second named element from a position defining an orifice of maximum area, means for adjusting the second named element to define initially an orifice of maximum area, rel asable means normally tending to rotate the second named element to reduce the orifice area, means for releasing the last named means at the beginning of the interval, speed-governing means controlling the releasable means to rotate the'sec- 0nd named element uniformly with time throughout the interval and means for indicating at the end of the interval the difference in fluid pressure of the containers.

7. In an averaging device for amovable member varying in position, means for determining the difference between an initial position of the memher and the average position thereof over a given time interval comprising two fluid-filled containers capable of varying in volume in response to applied pressure, a valve interconnecting the con tainers, a resilient means for converting deviations of the member from its initial position into corresponding variations in pressure on at least one of the containers, means for progressively closing the valve during the time interval to increase the time required for equalizing a continued difference in the pressures of the containers at a rate directly proportional to the time elapsed since the beginning of the interval to produce at the end thereof a final difierence between the pressures of the containers representing the accumulated average throughout the interval of the deviations of the member from. its initial position, and indicating means responsive to the final pressure difference.

ARTHUR L. HOLCOMB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 397,695 Clough Feb. 12, 1889 970,368 Frahm Sept. 13, 1910 1,066,125 Leming July I, 1913 1,085,012 Bopp Jan. 20, 1914 1,783,251 Man et al Dec. 2, 1930 1,862,259 Gargan June 14, 1932 1,881,266 Giers Oct. 4, 1932 2,142,124 Gardner Jan. 3, 1939 2,196,285 Bachle Apr. 9, 1940 2,232,198 Ashworth Feb. 18, 1941 

